Keliber Oy aims to produce battery grade lithium hydroxide for the international lithium battery market. Their operations are in Central Ostrobothnia area in Finland. Keliber has carried out spodumene beneficiation processes including calcination. Timegate Instruments has provided measurement and monitoring services to help optimize this high temperature process.
Furthermore, Timegate has carried out real-time process monitoring measurements with Keliber´s slurries at GTK Mintec Pilot Plant. This case study introduces these experiments.
What is the advantage of time-gated Raman spectroscopy with spodumene studies?
Elemental analysis, such as XRF or LIBS, are commonly used methods for analysing the elemental composition of process streams. As mineral processing is based on separating of minerals, not elements, direct mineralogical information is often invaluable.
Time-gated Raman spectroscopy provides a novel approach for mineral identification with direct mineral analysis from the process streams. Raman analysers can be directly attached to the process lines for measuring bypassing materials online in real-time without a need for taking samples.
Spodumene, like many other silicates, produces high intensity peaks in the Raman spectrum. Keliber’s spodumene beneficiation process was identified as a very promising monitoring application for time-gated Raman spectroscopy.
Real-time slurry monitoring at GTK Mintec
The measurements were carried out at GTK Mintec facilities using two MonitOre instruments equipped with 532nm pulsed lasers. The excitation laser light was delivered to the slurry, and the scattered Raman light was collected using two optical fibers connected to an industrial-grade Raman immersion probe for process integration.
Keliber Oy is a Finnish mining and chemical company with an aim of producing battery grade lithium hydroxide for the needs of the growing international lithium battery market.Keliber Oy
Two process points were monitored using immersion probes attached to different mixing units. One unit was measuring the waste line and another unit was measuring the product line containing a high concentration of spodumene. The on-line measurements were focused on determining the relative spodumene concentration by detecting the spodumene / feldspar+quartz Raman signal ratio (figure 1).
Figure 1. Simultaneous monitoring of spodumene / feldspar+quartz ratio from product and waste lines for 10 hours.
When the spodumene / feldspar+quartz ratio increases, the relative spodumene concentration increases and vice versa. At the beginning of the day, before the process was balanced out, the relative concentration of spodumene was low in the product line while it was quite high in the waste line. After process stabilization, the spodumene level increased in product line and decreased on the waste line.
The possibility to acquire real time and on-line monitoring data of changes in mineral concentrations in the process streams (incoming and outcoming material) are valuable information for the process control and adjusting of key processing parameters such as chemical or air feed. Additionally, real time monitoring may provide valuable information about process imbalances and prevent total process failures and breakdowns.
Converting α-spodumene to β-spodumene enables effective lithium extraction from the spodumene crystal structure. Timegate measured spodumene conversion rate during batch kiln furnace tests in which α-spodumene concentrate was heated up to 1025 – 1075°C temperatures. Spodumene conversion from α- to β-form occurs in this temperature range. In this case, process samples were taken every 5 minutes and the conversion degree (figure 2) were detected with a Timegate Raman spectrometer setup.
Figure 2. Conversion from α- to β-form at 0, 5, 10 and 15 minutes. While the amount of α-spodumene decreases, the amount of β-spodumene increases. The highest intensity α- and β-spodumene signals are pointed out in the figure.
Time-gated Raman spectroscopy is not sensitive to background thermal emission interference due to very short 100 picosecond laser pulse periods and time-resolved data collection. Read more about high temperature Raman measurements in our blog.
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